The application relates to an inspection microscope for a plurality of wavelength regions having at least one illumination beam path and at least one imaging beam path.
The invention also relates to a reflection-reducing layer for an inspection microscope for a plurality of wavelength regions.
In the semiconductor industry, inspection microscopes are used to observe, examine and test wafers, masks and semiconductor modules for monitoring the various fabrication steps. Inspection microscopes are generally substantially automated. They include, inter alia, automatic conveying and handling systems for the wafers or modules which are to be examined, as well as the possibility of automatic focusing.
It is known that the optical resolution of a microscope is dependent on the wavelength of the illumination light and on the objective numerical aperture. Since the objective numerical aperture cannot be increased arbitrarily, ever shorter wavelengths of the illumination light are being selected in order to resolve ever smaller structures. Therefore, ultraviolet light is used for resolution of the very small structures on wafers for large scale integrated circuits. Currently, illumination wavelengths of between 248 nm and 365 nm are customary in inspection microscopes.
Document 199 31 954 A1 describes an inspection micro-scope which operates with a plurality of wavelength regions. The light source used is, for example, a mercury vapor lamp with spectral components in the different wavelength regions. The wavelength regions in question are: firstly the visible wavelength region up to approx. 650 nm, referred to as the VIS region (short for “visible”), secondly the lamp line of the mercury vapor lamp which is known as the “i line”, with a wavelength λi line=365 nm, and thirdly a narrow wave-length band between approx. 200 and 300 nm from the deep ultraviolet wavelength region, also referred to below as the DUV region for short. The DUV wavelength band, which is characterized by its spectral peak value position and its half-intensity width, is filtered out of the light spectrum of the light source using a reflection filter system.
The illumination optics and the imaging optics of the microscope are corrected and modified for all three wavelength regions. The microscope image for the VIS region is displayed by means of eyepieces or in addition a camera for the VIS region. The microscope image for the i line and the DUV region is made visible using a UV-sensitive TV camera.